Final answer:
The primary ecological factor that likely contributed to the mass extinction of dinosaurs is a significant climate change, particularly cooling and drying of the climate, likely exacerbated by the impact of a comet or asteroid.
Step-by-step explanation:
The ecological factors that may have caused dinosaur extinction include options such as cooling and drying of climate, glaciation, and potential events like forest fires. The most prevalent theory among scientists for the mass extinction at the end of the Cretaceous Period is the impact of a large comet or asteroid. This impact is believed to have caused climatic disturbances, such as darkening skies, interruption of photosynthesis, and significant shifts in climate. Other contributing factors might include various climactic events, like cooling and glaciation, suggested by the evidence from different mass extinctions in Earth's history.
While torrential rains and forest fires could have occurred, they are not considered principal causes of the end-Cretaceous extinction event. Therefore, option A, cooling and drying of climate, would be a plausible ecological factor that, together with the cosmic impact, might have led to the great dying of the dinosaurs, making it a correct choice.